2001 A4 - AWM - Drive By Wire

After searching and reading throughout the forums for ideas, I'm still baffled at what my car is doing.

About 2 months ago, I was having issues with the car not starting sometimes, usually when hot. Let the car sit for a bit, and it would start back up and drive fine. One day it suddenly went into limp mode and then died on the freeway, and I had to pull over, let it sit for a while, then it started back up and I drove it home.

After that, I replaced the Engine Speed Sensor (Crank Sensor). Car ran great for about 3 weeks, then did the exact same thing again, but this time it never started back up, so I had to tow it home.

To rule out a faulty new Crank Sensor, I picked up another new one and tried it out, but that didn't solve anything.

VAG-COM was spitting out codes for misfires and throttle actuator issues, so I picked up a new Throttle Body Assembly and Cam Sensor and threw them on. Nothing.

VAG-COM was then giving me ECU Power Relay codes, so I replaced the ECU Relay with a new one. Still nothing.

The ECU gets too hot to touch when we're trying to start the car, but I've read that this is normal, apparently?

Here's where things get strange...

If I turn the key to the "run" position, I don't get a CEL on the dash, and the car won't start. If I turn the key to "run", then unplug the ECU Relay, the CEL comes on and fuel pump primes, then I can plug the relay back in and the car starts up. It idles like crap because the Throttle Adaptation doesn't happen, and I can't make it happen with VAG-COM, it just shows "ERROR".

I'm hoping that fixing the weird ECU issue will in turn allow the Throttle Adaptation to work, too, but I'm at a loss of where to go from here. I'm guessing that trying a different ECU is the next step, but it's an expensive step, so I want to explore every avenue before I do that.

Thanks for any help.

 

When my car is off and I turn the key to 'on' the CEL is on, but once I start the car is on its gone. (The same thing with my motorcycle - before it's actually running it's yells at me that oil pressure is low but once it's on its fine).

Are you not getting coolant temp codes? You're describing the exact symptoms of a bad Coolant temp sensor.

 

The coolant temp sensor was replaced recently, and I verified that it was working correctly with VAG-COM.

Ignition switch was also replaced recently, just for the record.

Took the ECU out of the case and checked the chips with a pyrometer. Everything stays within pretty reasonable temperature ranges with the exception of one chip. The chip in the red box gets to roughly 300 degrees F while the car is on. I've included a closeup of the toasty chip.

New ECU is on it's way, just don't want something else to fry the new one if it's something outside the ECU that's faulty.